Semiconductor device and manufacturing method of semiconductor device

Abstract

A semiconductor device is provided with: a first conductivity type contact region; a second conductivity type body region; a first conductivity type drift region of; a trench formed through the contact region and body region from a front surface of the semiconductor substrate, wherein a bottom of the trench is positioned in the drift region; an insulating film covering an inner surface of the trench; a gate electrode accommodated in the trench in a state covered with the insulating film; and a second conductivity type floating region formed at a position deeper than the bottom of the trench, and adjacent to the bottom of the trench. The floating region includes a first layer adjacent to the bottom of the trench and a second layer formed at a position deeper than the first layer, wherein a width of the first layer is broader than a width of the second layer.

The invention claimed is: 
     
       1. A manufacturing method of a semiconductor device, the method comprising:
 forming a trench extending from a front surface of a semiconductor substrate in a depth direction; 
 injecting impurities of a second conductivity type to a bottom of the formed trench by first injection energy; 
 forming a first protective film covering at least a side surface of the trench after the impurities of the second conductivity type had been injected to the bottom of the trench; and 
 further injecting impurities of the second conductivity type to the bottom of the trench by second injection energy that is larger than the first injection energy, after the first protective film had been formed, wherein: 
 the injection of the impurities by the first injection energy includes (i) injecting impurities of the second conductivity type in a state where no protective film is formed on at least the side surface of the formed trench, or (ii) injecting impurities of the second conductivity type in a state where a second protective film, that is thinner than the first protective film, is formed on at least the side surface of the formed trench; and 
 a bottom surface of a first region formed by the injection of the impurities of the second conductivity type by the first injection energy is in direct contact with an upper surface of a second region formed by the further injection of the impurities of the second conductivity type by the second injection energy. 
 
     
     
       2. The manufacturing method of a semiconductor device as in  claim 1 , wherein
 the first protective film is a sacrificial oxide film formed by oxidation of the front surface of the semiconductor substrate, and 
 the manufacturing method of a semiconductor device further comprises: 
 removing the sacrificial oxide film after the impurities of the second conductivity type had been injected by the second injection energy. 
 
     
     
       3. The manufacturing method of a semiconductor device as in  claim 1 , wherein
 the injection of the impurities by the first injection energy includes injecting impurities of the second conductivity type in the state where no protective film is formed on at least the side surface of the formed trench. 
 
     
     
       4. The manufacturing method of a semiconductor device as in  claim 1 , wherein
 the injection of the impurities by the first injection energy includes injecting impurities of the second conductivity type in the state where the second protective film is formed on at least the side surface of the formed trench.